A quiet little spot where Rod Mollise shares his adventures and misadventures...

Sunday, June 17, 2012

Woodstock vs. Yoda: The Thrilla in Possum Swamp

I love the StarBlast, Orion’s (Synta’s) 4-inch f/4 mini
Dobsonian reflector. It is easier to get outside for spur of the moment looks
at the night sky than any other telescope I own. But it’s not perfect, muchachos.
It has to be collimated every once in a while, and it has a major drawback
even—or maybe especially—for my uber-casual observing: cool down.

My grab and
go scope, which is supplemented by an humble but loveable pair of Burgess 15x70
binoculars, is not used for complicated and challenging observing projects, but
it does need to be able to present a passable image of a planet, since that’s
what I usually use it for, a casual look at Jupiter, Mars, Saturn, or the Moon.
And it’s got to be able to do that quick like a bunny.

Most of the
time I am taking the scope from the warm house into the cold (for us) outside
or from the cool house to the hot outside. It takes the StarBlast’s mirror a
while to acclimate before it can begin delivering the good images it is capable
of delivering. Even its wee 4-inch primary can take half an hour under the
worst conditions, and that does not fit into the spirit of Chaos Manor South
Guerilla Astronomy.

If I decide
I want to take a look at old Jupe during a commercial while I’m watching Doomsday Preppers, I want to be able to
do just that. I don’t want to haul the scope outside and wait for it to behave.
I could put the StarBlast on the porch ahead of time, but I don’t usually plan
my homebound observing in advance—not hardly.

I had a
partial solution, I thought, Eloise, my SkyWatcher 80mm f/11 achromat,
which I received “free” when I bought the Synta/SkyWatcher AZ4 mount. Eloise is
pretty good optically, surprisingly good as a matter of fact. Being a refractor, she’s ready to go with zero
cool down. But, like the StarBlast, she is not perfect; that long tube has
proven to be an annoyance bordering on a problem. When I want to take a
2-minute peep at The Ringed One from the front porch, it’s a pain maneuvering
her out the door on her mount.

“OK, then,”
Unk ruminated, “How about Woodstock?”
My Short Tube 80 refractor, that is, whose coming to Chaos Manor South a dozen
years ago was documented here. The 80 was my
original grab ‘n goer and I loved the little telescope. But Yoda, the StarBlast, had more aperture
and didn’t need a fussy GEM mount, and soon superseded if not obsoleted
Woodstock. I continued to use the little feller for various tasks like Solar
observing and guiding, but with the dearth of Sunspots over the last several
years, and my acquisition of one of Orion’s cool
50mm guide scopes, poor Woodstock hadn’t been out of his case in… A year? Longer?

I was
thinking the grab ‘n go sitchy-ation over the other afternoon when I ran across
the small box that contains my 3-inch Thousand Oaks (white light) Solar filter,
the one I used with Woodstock to take peeps at Sol during the last Solar Cycle, and
which I continued to use on Eloise when she came to the Old Manse. Took a look
at spaceweather.com, “Hmm…nice sunspot group has come back around. Why not have
a look at it? Why not have a look at it
with the Short Tube 80to see how
that silly little bird compares to the longer 80?”

Since I
didn’t want to fool with the EQ-2 GEM, I thought I’d see if I could mount
Woodstock on the AZ-4 mount. Ought to be easy enough to waltz the alt-az rig out
the door, even with its legs extended, with a shorter tube telescope riding on
it. I’d already been cogitating on how to mount the Short Tube 80 on the AZ4,
and in two shakes of a lamb’s tail, Woodstock was perched on the mount. The Short
Tube came with a ¼-20 mounting bracket onto which you can bolt the tube rings
that normally go on the scope’s EQ-1 German mount. I did that and screwed a
Vixen compatible dovetail onto the mounting bracket with a ¼-20 bolt.

It was indeed
easy to get the little 80 out of the house and onto the front porch without
doing major damage to furniture or telescope. I soon had the Solar filter in place and was checking
out the Sun with a 12mm Plössl. Not bad. Not bad at all. Sharp, with the most
prominent sunspot showing not just its dark bb-like umbra, but a fairly
extensive penumbra too. All well and good. How would the 80mm f/5 compare to the
80mm f/11?

I switched
out Woodstock for Eloise, attached the filter, and inserted a 26mm ocular,
which would yield a comparable magnification to that of the Short Tube 80.
“Hmm…lots of smaller spots I didn’t notice with the ST80.” Back on the mount went
the 80. Focusing more carefully—focus is much
shallower with a fast scope—brought out most of the spots I’d seen with the
f/11. I still thought the image in the higher focal ratio scope was sharper,
but maybe it was only a little sharper.

Might it be
time to let Woodstock take up his long-lost duties as Chaos Manor South’s
official grab ‘n go scope again? Perhaps. But the StarBlast, Yoda, wouldn’t go
down without a fight. Years back, shortly after the StarBlast arrived, I’d had
a shootout between him and the Short Tube 80 in Chaos Manor South’s backyard. It
looked like it was time for a rematch.

The Contendas:

In this
corner, we have Woodstock, the Synta Short Tube 80 achromat, riding on a
single-arm Synta AZ4 alt-azimuth mount. Woodstock has not been in the ring in a
while, but is still in fighting trim, with clean optics and a focuser that—I
was surprised to note—is still smooth and easy after years of disuse. His
aperture is 80mm and his focal ratio is f/5. On his tube is a minimalist but surprisingly
good 30mm finder.

In the other
corner is Yoda, a Synta StarBlast Newtonian reflector weighing in at 114mm of
aperture. His mount is a smooth and very functional single-arm Dobsonian that
features an adjustable tension, ball-bearing race-equipped altitude axis and
Teflon-on-Formica bearings for azimuth. His finder is one of Orion’s ubiquitous
(and overpriced) “EZ Finder II” red dot jobs.

The Eyepieces:

Both
telescopes have 1.25-inch focusers, and the Short Tube 80 is equipped with a
star diagonal, of course. Any number of eyepieces could have been used for this
shootout, up to and including my 1.25-inch capable TeleVue 8mm and 13mm Ethoses,
but I thought the 20, 15, 9, and 6mm Orion Expanse 66-degree AFOV eyepieces
were more in keeping with the simple, inexpensive nature of the contestants.
For lower powers, I used a classic Celestron Silver-top Plössl of 26mm focal
length. When higher powers were called for, a 2x Orion Shorty Barlow and a 3x Knight
Owl ED Barlow were used with the Expanses as necessary.

The place to
test the mettle of the telescopes was obviously Mars, which was just past
opposition at the time of the bout. It’s a challenge for any scope, since it is
small even at its closest and most of its features are of a distinctly low contrast
nature. I’d been rather impressed by how well the StarBlast had done on it a
week or two previous, and wondered if the Short Tube 80 could possibly keep up.
I did recall I had some excellent views of Jupiter when Woodstock was new. I’d
seen the disk of Io transiting Jupe’s face—the disk, not just the shadow—so I
wasn’t ready to count him out. While waiting for The Angry One to clear the
trees, I sent both telescopes to the Moon.

Round 1

26mm Plössl = 15x in Short Tube, 17x in StarBlast

I started out
at low power, if not at the lowest power I could have mustered—I’ve got a 40mm Plössl
around here somewheres. One of the major attractions of these two richest-field-telescopes
is, after all, their extremely low power, wide field capability, and I wanted
to give both a chance to show that off.

Short Tube
80: What a lovely image of a nice,
gibbous Moon! Framed by a huge expanse of sky and the chimney top of the house
next door, it was just exquisite. The terminator was dead sharp. “But how about
the COLOR, Unk? How about the dreaded color purple?” Chromatic aberration is
always the 64 dollar question when talking “achromat,” especially “fast
achromat,” ain’t it? There was some color, but it wasn’t purple. With my eye on
axis, there was a fairly subdued amber fringe along the limb. Placing my eye
off axis, it took on a purple hue, but was not at all disturbing.

If you are
going to have a fast optical system, which is what most of us want in a grab ‘n
go, you are likely gonna have some field curvature and/or coma. How was Woodstock?
Moving the Moon around in the field, I found the image was pretty sharp in the
simple-design eyepiece till about 70% of the way to the field stop. Even past
there it was OK, if not razor sharp.

StarBlast: The eyepiece delivered slightly higher power
in the StarBlast, but in most ways the image was identical to what I’d seen in
the refractor. Good and sharp. Excess color? There was none. And I don’t just
mean there was no amber or purple stripe along the limb, but that the whole disk of the Moon looked truer in
color. In the Short Tube, the Moon had a slight but noticeable yellowish
tint, but in the StarBlast it was a pure, silvery hue that just looked more
natural and “better” in comparison.

On the other
hand, the coma inherent in a fast reflector assured that the refractor pulled
ahead in the edge-of-field department. In the StarBlast, the image began to go
mushy about 50% of the way from the center of the field, and at the edge it was
rather icky indeed. I also noticed the fairly obvious shadow of the StarBlast’s
secondary mirror with this bright target at such low power.

Woodstock was victorious in Round 1.
Despite the reflector’s lack of color, the refractor took the laurels due to
its flatter field and lack of a secondary shadow.

Round 2

15mm Expanse
= 27x in Short Tube 80, 30x in StarBlast

At 27x, the
image of the Moon delivered by the Short Tube was still amazingly sharp. The
higher magnification began to bring out details, too, like the terracing of the
walls of the great crater Copernicus. Chromatic aberration? No more than what
was seen at 15x.

The 30x
image in the StarBlast was unmistakably brighter than the 27x image in the
refractor. Otherwise? The level of detail visible on the terminator was about
the same as that in the Short Tube 80. Once again, the color appeared more
natural in the reflector than in the refractor. I only tended to notice that
when I moved back and forth between the telescopes, though.

Round Two was judged to be a tie…

Round 3

9mm Expanse
= 44x in Short Tube 80, 50x in StarBlast

At 40x, a
good scanning/casual observing power, the refractor was still delivering the
goods—and how. The terminator was an amazing welter of tiny details, with
Gassendi, where the Sun was just rising, looking impressively sharp. How about
areas of the disk away from the terminator? Looking good. The maria stood out
with decent contrast. Unfortunately, chromatic aberration was becoming more obvious. Color fringing on the limb was harder to
ignore, and I thought I detected a hint of purple in the shadows of the
terminator detail. Not crazy bad, but
there.

Yoda
laughed. This is where the StarBlast began to pull ahead. Not only was the
absence of spurious color immediately obvious, the terminator detail was good
and sharp. It was sharp in the refractor, but it was just a little sharper in
the reflector. I also noted that the detail on the disk away from the
terminator, Tycho’s ray system for example, was higher in contrast and easier
to see in the StarBlast.

Round Three went to Yoda, but just
barely…

Round Four

6mm Expanse
= 66x in Short Tube 80, 76x in StarBlast

Kicking up
the power a notch delivered more detail with Woodstock. Small detail, like the
craterlets that litter the floor of Clavius, popped right into view. I liked
the look of it a lot. Alas, away from the day-night line, the disk was looking
decidedly soft. Not bad, mind you, but not quite as sharp as at lower power.

At 76x, the
level of detail visible with Yoda was impressive. Copernicus, with his complex
central peak and fascinating walls, was just nuts. The arc of small craters in Clavius was visible in the
refractor, but it was sharper in the reflector, and I was able to see some
smaller features on the crater floor that were not apparent in the ST80. The
disk away from the terminator looked every bit as good as it did at lower
power—much better than in the Short Tube, in other words.

Round Four was given to Yoda, and it
wasn’t even close…

Round five

6mm Expanse,
2x Barlow = 133x in Short Tube 80, 152x in StarBlast

Little
Woodstock was still on his feet, but was looking wobbly. The Short Tube 80’s image,
including the terminator, was getting undeniably soft. Surprisingly, chromatic
aberration, though certainly noticeable, didn’t look much worse than it had at
66x. Despite the slight softening, there was plenty of detail to be seen.
Gassendi was looking very complex. Offsetting that, the image was now also on
the dim side.

Yoda? At
this magnification, Luna in the StarBlast reminded me very much of the way it
looked back in the day in my long focal length Palomar Junior 4.25-inch
reflector. Tons of detail on view everywhere and as sharp as ever.

If Woodstock
was wobbling before, he was stumbling now. The Moon’s image was soft overall,
softer than ever, and I wasn’t seeing any more detail than I had at lower
power. Surprisingly, color was still under control. 200x was somewhat useable, and might have been a
wee bit better with better seeing, but it was a lot to ask of this f/5
achromat.

Yoda laughed
again. He took on 228x without complaint and seemed ready for more. The image
was getting dimmer—this is a 4-inch
telescope—but it was still astoundingly sharp. The bright spot on the floor of
Plato that marks the most prominent of his craterlets winked right into view.
Gassendi was superb and so was Clavius, and I was definitely seeing more detail
than I had at lower power.

Round Six was another victory for
Yoda. The referee considered stopping the fight, but Woodstock begged to be allowed
to go on…to Mars…

Round Seven

Due to the
depredations of clouds, Mars had to wait till the next night. When Barsoom put
in his appearance, it didn’t take long to determine what was what. Let’s make
this short and sweet: The Angry Red Planet laid Woodstock out on the canvas. At
about 100x, the image was pretty good, but that was far too little
magnification to do more than just show the bright red “star” was indeed Mars.
Pumping it up to 200x, just enough magnification to reveal details, made the
disk of Mars a mess. No combination of eyepieces or Barlows helped. The small
refractor was well and truly done.

So the
victor was the StarBlast? Sorta. Yoda disappointed a little bit. Yes, at 200x,
the image was much cleaner than in the 80. I could see the polar cap, and I
could see hints of dark features, but it was clear the scope needed at least a
little while to adjust to outdoor temps. The image was good, just not as good
as I knew it could be in this amazing little scope.

The real and
surprise winner, I guess, was the 80mm f/11 refractor. On a whim, I hauled her
out, and Eloise produced simply outstanding images given her aperture. Even at
300x, Mars was a good-looking ball showing fleeting surface detail and a polar
cap. I suppose the contest had morphed from a prizefight into a horserace with
the 80mm f/11 coming from behind to best the StarBlast by a nose.

So what now?
Status quo. The idea of resurrecting
the Short Tube 80 was a good one, and I suppose he could do alright once in a
while, for a casual look at the Moon, maybe. But there is no denying he is the
weakest of the three telescopes. I reckon Yoda will remain the primary g ‘n g
scope at Chaos Manor South. But when I need top-notch images in a hurry without
cool down, I’ll just have to wrestle the 80 f/11 out the front door.

I’m not sure
there is a perfect grab ‘n go for me.
It would have to be something like a short and light 4 – 5-inch APO refractor,
and even if I found one short enough and light enough to serve, I probably
wouldn’t want to pay for it. If I
ever do achieve grab and go nirvana, I guar-ron-tee y’all will be the first to
know about it, muchachos.

Rod great blog , small scopes are fun great during the work week, have you ever tried to get a used Brandon 94 for grab and go? You can use it on a VIxen Porta or as I have done on a quarter half hitch mount. The C90 ( orange tube vintage) is also a great grab and go! These scopes are good if you live in an area with fleeting Weather conditions.best Regards ,Satman cloudy nights classic Telescope forum

Hi Rod. For Grab n Go, how about that WO Megrez90 you used to have? I have one on a Vixen Porta mount and its great for when I can't be bothered to set up the Big Boy. I often like to see how far I can get with Chuck Wood's Lunar100 (the higher the number, the harder the the target) and the M90 can do suprisingly well. It's also good for having a quick review of the celestial highlights of the night/hour. It does weigh a bit though, so it's not something to sling over your shoulder and jog up the nearest mountain with. It is an absolute joy to use but I have to say that for the money, you can get much more aperture so I wouldn't recommend as a main scope, especially for DSO's where there is a bit of light pollution to contend with.

For grab&go I too use an St80 but with a 2" focuser. This allows fitting of the bottom element of a 2" GSO Barlow and a minus-violet filter both within the focuser tube. Coupled with a 2" GSO diagonal it makes for a great travel scope, and breaks down easily for carrying as airplane hand baggage. An SLT go-to mount is a fairly lightweight companion for checked baggage, and an alt-az manual for faster access when manually tracking with a solar filter.

For grab&go I too use an St80 but with a 2" focuser. This allows fitting of the bottom element of a 2" GSO Barlow and a minus-violet filter both within the focuser tube. Coupled with a 2" GSO diagonal it makes for a great travel scope, and breaks down easily for carrying as airplane hand baggage. An SLT go-to mount is a fairly lightweight companion for checked baggage, and an alt-az manual for faster access when manually tracking with a solar filter.

I think that if you had added one of the Synta 80ED's, like the Skywatcher or Orion, it would probably best Yoda and Woodstock both, and would have wider fields than Eloise and similar sharpness. Have you tried one? The shootout continues...

I had to agree to sell my ST80 in order to have Hubby agree to let me buy my ETX-80. And frankly, the ST80 hasn't been used much since I bought my C5, which is a great g n g scope even if not really cooled down. I can move it outside on its CG-4 mount in one piece without disassembly.

BTW, I tried to post comments several times on your filter reviews, but they never appeared. I think there may be a bug there.

Thanks, Unk, for an excellent writeup. This is extremely useful stuff.

One thing I've always liked about small reflectors is that you can fiddle with the collimation while looking through the eyepiece. It certainly helps short f/l scopes like the StarBlast punch above their weight.